One type of a widely used surgical device is a tool for retrieving foreign material from various sites along the urinary tract of a patient's body. Examples of the foreign material include calculi of different sizes and characteristics.
Referring to FIG. 1, a schematic view, partially in a longitudinal cross-section of the distal end of an example of a conventional surgical retrieval tool is illustrated. The surgical retrieval tool 10 or so-called surgical extractor, generally comprises a flexible tubular catheter 11 formed as a tubular sheath adapted to penetrate the body passages to reach the location where the object (not shown) to be evacuated is located. A manipulation rod or cable 12 is located within the catheter 11, which can be manipulated from the outside at the catheter's proximal end. The rod 12 is coupled to a basket 13 capable to be deployed within the sheath. The basket 13 consists of flexible filaments 14 and, for example, can be made of either stainless steel or any other material capable to provide the basket with elasticity. According to the example shown in FIG. 1, the filaments 14 are bound together in the vicinity of a basket proximal end to form strands 19 as well as at a basket distal end to form a tip 15. The basket 13 is usually connected to the manipulation rod 12 via a sleeve connector 17 bounding the strands and filaments together.
One of the drawbacks of the conventional surgical extractor is associated with the discrepancy of the inner diameter of the catheter 11, the diameter of the manipulating rod 12 and the diameter of the connector 17. Due to this discrepancy, an air gap 18 between the inner wall of the catheter 11 and the rod 12 significantly affects deformation properties of the catheter and the ability of the catheter to bend without destruction on large angles.
Depending on the manipulation, the basket 13 may either retract inside the sheath to allow penetration of the catheter via a passage or protract from the catheter. In the protracted position, the filaments open due to the elasticity of their material and form a cage to thus allow entering the object inside the basket 13 through the open spaces 16 left between its adjacent filaments. Further retraction of the basket inside the sheath results in the cage collapsing and entrapping the object in the basket. Removal of the catheter will enable the whole device to be removed from the body organ together with the object immobilized within the basket.
During an operation, the surgeon moves the catheter behind the object to be extracted, and then protracts the basket from the catheter. Once the basket is protracted it opens (due to its resiliency) and is ready for receiving the object to be entrapped therein. The surgeon pulls the catheter together with the basket until it entraps the object, and thus extracts the entrapped object from the body.
It can be easily appreciated that the particular design of the basket is crucial for entrapping and reliably retaining the object during evacuation. Examples of various types of such retrieval baskets are described in the following documents: U.S. Pat. Nos. 2,943,626; 3,137,298; 3,472,230; 4,299,225; 4,347,846; 4,590,938; 4,633,871; 4,611,594; 4,790,812; 5,057,114; 5,496,330; 5,064,428; 5,658,296; 6,168,603; 6,183,482 and 6,190,394.
It should be noted that generally all conventional retrieval baskets have certain common characteristics. Thus, each retrieval basket comprises a plurality of filaments and can be collapsible into a compact form. The filaments are formed from wires and can be arranged into either multi-filament strands or spaced single filaments.
There are known the baskets that have relatively few widely spaced multi-filament strands at the proximal basket end, for capturing the object. These baskets may include two or more such multi-filament strands between which the objects can pass for entrapping within the retrieval basket. On the other hand, the filaments are closely spaced in the vicinity of the distal basket end, to provide an enclosure for retaining objects captured within such retrieval baskets. In some retrieval baskets the strands are formed along substantially straight lines when the basket is in compact form; in others, the individual strands extend along a generally helical path.
Forming the conventional baskets generally comprises grouping a plurality of axially extending filaments, strips or wires having shape memory or superelastic properties to extend along the basket axis and bounding them together at distal and proximal basket ends between which each of the wires extend.
In order to increase the number of contacts between the basket and entrapped calculi, additional filaments would be advantageous. However, an inner diameter of the catheter imposes an upper limit on the filament number and their diameter. Thus, for sufficient strength of the basket, the basket design involves a compromise between the number of filaments (needed to retain objects and enable the capture of the objects) and the wire diameter.
It can be appreciated that rigid wire materials can be employed in order to enhance the strength of the basket. However, the utilization of rigid materials can result in a decrease in flexibility that is necessary to provide penetration of the basket in body tracts having small diameters, tortuous pathways and irregular lumens.